U.S. Pat. No. 6,803,958 discloses that, when performing photoelectric conversion to light incident from a photodiode thereby converting an obtained analog signal to a digital signal in an image sensor circuit, it is required to remove noise from an image signal.
However, when converting to the digital signal, there is a problem that digital conversion is not performed to a reset signal, which is a reference voltage of the image signal out of the analog signal, due to magnitude of a gain of a reference signal, and an entirely black and dark image is obtained.